Mold for air-slip type noncircular continuous casting and casting method of aluminum alloy using the same

ABSTRACT

The present invention relates to a mold for air-slip noncircular continuous casting and a casting method of aluminum alloy using the same. The mold of the present invention includes a mold body  20  having a noncircular through hole  10  which allows molten metal  80  to move therein; a porous graphite ring  70  provided on an inner circumference of the mold body  20  to supply gas and oil to a surface of the lowering molten metal  80  metal thereby solidifying the molten metal  80  into a billet; and a conveying plate  95  provided on the inner circumference of the mold body  20  on top of the graphite ring  70  to convey the molten metal  80  downward, wherein a cooling water chamber  60  is formed in the mold body  20  to store cooling water for cooling a surface of the billet, the cooling water chamber  60  being formed in the rear of the graphite ring  70 , and a gas inlet  32  and an oil inlet  34  are connected to an upper end of the graphite ring  70  to respectively supply gas and oil into the graphite ring  70  through the mold body  20 . According to the present invention so configured, it is possible to enhance durability of the mold and allow production of an aluminum alloy with uniform composition when casting an aluminum alloy with a noncircular cross section.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mold for air-slip noncircular continuous casting and a casting method of aluminum alloy using the same.

2. Description of the Related Art

In currently produced billets dedicated to aluminum extrusion, an air-slip type continuous casting method is mostly adopted, thereby providing excellent effects owing to its various advantages. However, the air-slip method is advantageous for aluminum casting of a circular cross section, but it shows various problems when being applied to a noncircular cross section.

Here, in the air-slip method, a mixture gas (nitrogen and oxygen) and oil are directly supplied to a billet surface through a porous graphite to previously control heat emission caused by direct contact between molten metal and a mold, differently from a conventional direct cooling method.

FIG. 1 is a sectional view illustrating that a billet is produced in a mold assembly employed in the air-slip method. According to the figure, a molten metal through hole 1′ is formed vertically through a mold body 1. The molten metal through hole 1′ is a portion which is filled with molten metal 2 for producing a billet 9, which will be described below.

A graphite ring 3 is provided around an inner circumference of the molten metal through hole 1′. An inside shape of the graphite ring 3 becomes an outside shape of the billet 9. Since the graphite ring 3 is porous, so that lubricant and nitrogen and oxygen mixture gas are allowed to pass through the graphite and supplied between the billet 9 and the inner surface of the graphite ring 3, thereby minimizing friction between the mold and the billet. Reference numeral 5 designates a cooling water supplier.

A drawing unit 7 is positioned at a lower inner side of the molten metal through hole 1′ to be lifted and lowered. The drawing unit 7 allows a molten metal 2 positioned on the drawing unit 7 to be lowered through the molten metal through hole 1′ in a solidified state, so that the billet 9 is successively made to have a predetermined length.

In the mold assembly so configured, a molten metal 2 is supplied to the molten metal through hole 1′ in a state where the drawing unit 7 is lifted as much as possible to the lower portion of the molten metal through hole 1′. The molten metal 2 starts to be solidified on the drawing unit 7. In an initial casting stage, the drawing unit 7 is lowered constantly at a lower casting speed than a maximum casting speed so as to keep stability of the solidifying interface.

However, the above prior art has problems as follows.

That is, when the conventional air-slip method is used for aluminum casting with a noncircular cross section, the casting work is substantially impossible. This is because the graphite ring of the casting mold is integrally configured through a shrink fitting process, is deformed in shape due to the nature of the noncircular shape when the graphite ring is thermally deformed, and thus escapes from the casting mold.

Further, in the prior art, since oil and gas is supplied from a side of the graphite sing, a gap is generated between the graphite ring and the mold body due to the pressure of gas and oil. Thus, the oil and gas are not smoothly supplied to the graphite ring, which results in unstable generation of air slip.

SUMMARY OF THE INVENTION

The present invention is conceived to solve the aforementioned problems in the prior art. An object of the present invention is to provide a stable air-slip type continuous casting mold, capable of minimizing deformation caused by heat of a graphite ring used in an aluminum alloy casting mold of a noncircular cross section without using a shrink fitting process of a graphite ring which was used in a conventional air-slip type circular mold.

According to an aspect of the present invention for achieving the objects, there is provided a mold for air-slip type noncircular continuous casting, comprising: a mold body having a noncircular through hole, the noncircular through hole allowing molten metal to move therein; a porous graphite ring provided on an inner circumference of the mold body to supply gas and oil to a surface of the lowering molten metal thereby solidifying the molten metal into a billet; and a conveying plate provided on the inner circumference of the mold body on top of the graphite ring to convey the molten metal downward. A cooling water chamber is formed in the mold body to store cooling water for cooling a surface of the billet, the cooling water chamber is formed in the rear of the graphite ring, and a gas inlet and an oil inlet are connected to an upper end of the graphite ring to respectively supply gas and oil into the graphite ring through the mold body.

At this time, the cooling water chamber may be formed such that an upper end of the graphite ring is higher than a lower end of the cooling water chamber and a lower end of the graphite ring is lower than an upper end of the cooling water chamber.

Alternatively, the cooling water chamber may be formed such that an upper end of the graphite ring is lower than an upper end of the cooling water chamber and a lower end of the graphite ring is higher than a lower end of the cooling water chamber.

In the meantime, the mold body may include an upper body defining an upper portion of the chamber and having a lower surface supporting an upper surface of the graphite ring, the upper body being formed with a gas inlet and an oil inlet for respectively supplying gas and oil to an upper portion of the graphite ring; a lower body defining a lower portion and an outer side portion of the mold body; and an inner body coupled with the upper body and the lower body to define an inner side of the mold body and having a seat portion formed on an inner circumference thereof to allow the graphite ring to be seated thereon.

Further, the graphite ring may have an upper surface supported by the upper body and side and lower surfaces seated on the seat portion of the inner body and fixed to the mold body.

Furthermore, an asbestos gasket may be provided between the graphite ring and the upper body.

In addition, the graphite ring may be divided into a plurality of pieces.

In the meantime, an inner circumference of the graphite ring may have a tapered shape whose width is widened as it goes downward to cope with the changed amount of billet that is changed by solidification contraction.

Further, the lower body may have cooling water discharge channels for supplying the cooling water of the cooling water chamber to the billet.

Furthermore, the cooling water discharge channels may be formed to have different diameters depending on the amount of heat generated from the billet, or to have different densities at every portion of the inner body depending on the amount of heat generated from the billet.

In the meantime, according to another aspect of the present invention, there is provided an air-slip type continuous casting method of aluminum alloy, in which molten metal is solidified while passing through an inner surface of a conveying plate and a graphite ring, thereby producing a billet with a noncircular cross section, the conveying plate and the graphite ring having a tapered shape and being installed on an inner surface of a noncircular through hole of a mold body. The method comprises the steps of: forming a film on a surface of the molten metal being solidified by gas and oil introduced from an upper portion of the graphite ring; cooling the graphite ring by cooling water of a cooling water chamber provided in the rear of the graphite ring; and allowing a borderline of the solidified billet and the molten metal to be in contact with an inner surface of the graphite ring.

Here, the billet may be cooled by the cooling water, the cooling water being supplied from the cooling water chamber and ejected through cooling water discharge channels in a lower portion of the graphite ring.

In addition, the cooling water may be ejected in different amounts depending on the amount of heat generated according to a shape of the billet to be cast.

Further, the amount of the cooling water may be determined by the number of the cooling water discharge channels, or by size of the cooling water discharge channels.

According to the mold for air-slip type continuous casting according to the present invention as described above, the following advantages can be expected.

That is, since the graphite ring provided in the casting mold is divided into a plurality of pieces and fixed to the mold body by mechanical coupling, the graphite ring is less deformed by heat, so that the graphite ring does not easily escape from the mold body.

Also, in the present invention, since the cooling water chamber is positioned at the rear side of the graphite ring, the graphite ring is cooled by cooling water of the cooling water chamber, thereby improving heat emitting efficiency of the graphite ring.

In addition, according to the present invention oil and gas is supplied to the upper portion of the graphite ring, whereby the graphite ring does not escape by the pressure of the oil and gas. Since the asbestos gasket is provided at the gas and oil inlets of the graphite ring, it is possible to prevent a gap from being generated between the graphite ring and the upper body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing major portions of a mold assembly in which a conventional air-slip type continuous casting method of aluminum alloy is performed.

FIG. 2 is a sectional view showing major portions of an air-slip type casting mold according to a specific embodiment of the present invention.

FIG. 3 is a plane view showing that a graphite ring is seated on a seat portion of an inner body of the casting mold according to the specific embodiment of the present invention.

FIG. 4 is a plane view showing the graphite ring according to the specific embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, a specific embodiment of an air-slip type continuous casting mold according to the present invention will be described in detail with reference to the drawings.

FIG. 2 is a sectional view showing major portions of an air-slip type casting mold according to a specific embodiment of the present invention, FIG. 3 is a plane view showing that a graphite ring is seated on a seat portion of an inner body of the casting mold according to the specific embodiment of the present invention, and FIG. 4 is a plane view showing the graphite ring according to the specific embodiment of the present invention.

As shown in the figures, the air-slip type casting mold according to the specific embodiment of the present invention includes a mold body 20 in which a noncircular through hole 10 is formed.

The through hole 10 has a shape corresponding to a cross section of a billet to be cast and may have various shapes. However, for convenience of description in this embodiment of the present invention, an L-shaped through hole will be described as an example (see FIG. 3).

Meanwhile, the mold body 20 includes an upper body 30 defining an upper portion thereof, a lower body 40 defining a lower portion and an outer side portion thereof, and an inner body 50 defining an inner surface thereof, which are coupled to each other. Of course, the mold body 20 is divided into the upper body 30, the lower body 40 and the inner body 50 so that the mold body 20 is easily assembled. Its combination structure may vary in different ways (for example, the mold body may be divided into two parts).

The upper body 30 defines the upper portion of the casting mold and has an inner end in contact with an inner surface of the inner body 50 and extending by a predetermined length. Accordingly, an end of the extending portion can support an upper surface of a graphite ring 70, which will be described later.

Meanwhile, a gas inlet 32 and an oil inlet 34, through which gas and oil are respectively injected, are formed in the extending portion of the upper body 30 such that the gas and oil are supplied to the upper surface of the graphite ring 70.

The lower body 40 is formed to have an “L” shape to define the outer side and lower portions of the mold body 20, wherein an upper end of the lower body is in contact with the upper body 30 and another end thereof is in contact with the inner body 50.

In addition, the lower portion of the upper body 30, the other end of the lower body 40 and the inner body 50 are coupled to each other. A seat portion 52 on which the graphite ring 70 to be explained later is seat, is formed on the inner surface of the inner body 50. The seat portion 52 is shaped corresponding to an outer circumference of the graphite ring 70 so that the outer circumference and a lower end surface of the graphite ring 70 may be seated thereon.

At this time, the upper body 30, the lower body 40 and the inner body 50 are firmly screwed to each other. Also, the upper body 30, the lower body 40 and the inner body 50 are coupled to thereby define a cooling water chamber 60 for storing cooling water, as shown in FIG. 2. Here, the size and position of the cooling water chamber 60 are related to the position of the graphite ring 70, which will be thus discussed after the graphite ring 70 is explained.

The seat portion 52 is provided with the graphite ring 70 that is porous. The graphite ring 70 is a portion where molten metal 80 passing through the mold is solidified into a billet 85. A surface of the molten metal 80 passing through the graphite ring 70 is solidified to form the billet 85.

At this time, an outer side of a borderline at which the molten metal 80 is solidified to form the billet 85 is preferably formed on the graphite ring 70.

Meanwhile, the graphite ring 70 allows the gas and oil introduced through the gas inlet 32 and the oil inlet 34 to pass through pores of the graphite ring 70 to thereby forms a film such that an outer circumference of the molten metal 80 being solidified does not physically contact with an inner circumference of the casting mold.

The outer circumference and the lower end surface of the graphite ring 70, which are seated on the seat portion 52 of the inner body 50, are preferably formed to have a curved surface.

The graphite ring 70 is seated on the inner body 50, which is shown in FIG. 3. As shown in FIG. 3, the graphite ring 70 is also formed with the noncircular through hole 10 and is seated on the seat portion 52 of the inner body 50.

As shown in an enlarged portion of FIG. 3, the upper end of the graphite ring 70 is supported by the upper body 30, not shown in FIG. 3, and the force by which the upper body 30 supports the graphite ring 70 is caused by a coupling force of the upper body 30 and the inner body 50. Coupling holes 54 through which the inner body 50 and the upper body 30 are screwed to each other are formed in the upper end of the inner body 50.

In addition, the outer side of the inner body 50, in which the cooling water chamber 60 is formed, is formed with cooling water discharge channels 56 through which cooling water is discharged form the cooling water chamber 60. Here, it can be seen from the enlarged portion of FIG. 3 that gaps between adjacent ones of the cooling water discharge channels 56 are different. It means that density of the cooling water discharge channels 56 varies depending on every region in the inner body. This is because the billet 85 has a noncircular cross section and thus the amount of generated heat varies depending on every region, so that the amount of discharged cooling water should be different so as to provide the same cooling effect at every region of the billet 85. That is, in order to control the amount of the cooling water, the cooling water discharge holes for ejecting the cooling water may be different in number from each other at every region according to the amount of heat generated from the billet 85.

That is, the amount of generated heat is relatively greater at an angled or edge portion than a plane or a curved portion, so that the cooling water should be more supplied to the angled or edge portion.

Meanwhile, the graphite ring 70 according to the present invention is configured to be divided into a plurality of pieces, as shown in FIG. 4. In the specific embodiment of the present invention, the graphite ring 70 that is divided into three pieces as shown in the figure is explained as an example.

The graphite ring 70 is formed not integrally but to be divided into the plurality of pieces due to the following reason. The graphite ring 70 of the present invention is fastened through not a shrink fitting process that is a conventional coupling manner of graphite ring 70 but a coupling manner using a mechanical coupling force, so that the graphite ring 70 may not have an integral shape and thus may be minimized in shape deformation caused by thermal expansion. That is, the divided-type graphite ring 70 is advantageous against thermal expansion, but the graphite ring 70 should be integrally formed in the conventional continuous casting mold since the graphite ring 70 is fixed through a shrink fitting process.

At this time, an asbestos gasket 90 is provided on contact surfaces of the upper body 30 and the upper end of the graphite ring 70 so as to prevent a gap from being generated between the contact surfaces. This is because the gas and oil introduced to the graphite ring 70 from the gas inlet 32 and the oil inlet 34 should be prevented from being mixed before being introduced into the graphite ring 70.

Meanwhile, the cooling water chamber 60 provided in the mold body 20 stores cooling water supplied to the billet 85. The cooling water chamber 60 is preferably formed in the rear of the graphite ring 70 at a level similar to the graphite ring 70 so as to cool the graphite ring 70 that receives high temperature heat during casting.

That is, the levels and heights of the cooling ring 70 and the cooling water chamber 60 are determined such that an upper end of the graphite ring 70 is higher than a lower end of the cooling water chamber 60 and a lower end of the graphite ring 70 is lower than an upper end of the cooling water chamber 60. More preferably, the upper end of the graphite ring 70 is lower than the upper end of the cooling water chamber 60, and the lower end of the graphite ring 70 is higher than the lower end of the cooling water chamber 60. That is, their levels and heights are determined that the graphite ring 70 with height L is positioned within a region defined by height 1 of the cooling water chamber 60.

At this time, the inner circumference of the graphite ring 70 may be formed in a tapered shape whose width is widened as it goes downward so as to cope with the changed amount of billet that is changed by solidification contraction. This shape allows the graphite ring not to interfere with the billet as the billet is contracted by solidification.

Meanwhile, in the specific embodiment of the present invention, a conveying plate 95 for conveying the molten metal 80 downward is provided on the inner circumference of the mold body 20. The conveying plate 95 is provided on top of the graphite ring 70, and may have a tapered shape whose width is widened as it goes downward to cope with the billet that is contracted by solidification.

Hereinafter, the operation of the specific embodiment of the present invention will be explained in detail according to the air-slip type aluminum continuous casting method.

In the air-slip type aluminum continuous casting method according to the specific embodiment of the present invention, the molten metal 80 is cooled while moving along the through hole 10 of the mold body 20.

Then, if the molten metal 80 reaches a position of the graphite ring 70, an outer side of the molten metal 80 is solidified to form the billet 85. At this time, a borderline 99 of the billet 85 and the molten metal 80 is shown in FIG. 2. Of course, the borderline 99 is a virtual borderline, and a border of the molten metal 80 and the billet 85 is not definite in practice.

When the billet 85 is formed at the position of the graphite ring 70, gas and oil are introduced from the inside of the graphite ring 70 to form a thin film on the inner circumference of the graphite ring 70. As the gas, nitrogen and oxygen gas is generally used.

The film formed on the inner circumference of the graphite ring 70 prevents the molten metal 80 from being in contact with the graphite ring 70 during its solidification and thus a surface of the molten metal 80 from being rough.

At this time, the outside of the molten metal 80 is cooled first and the inside thereof is cooled later, so that expansion pressure occurs from the inside to the outside. However, since the graphite ring 70 has the tapered inner circumference, the expansion pressure caused by the heat becomes removed together with volume expansion of the molten metal 80.

Meanwhile, the molten metal 80 or the billet 85 heats the graphite ring 70. At this time, the heated graphite ring 70 is cooled by cooling water of the cooling water chamber 60 that is formed in the rear of the graphite ring 70 with the inner body 50 being positioned therebetween.

In addition, as the billet 85 moves downward past the graphite ring 70, the billet 85 is cooled by cooling water discharged from the cooling water discharge channels 56 formed in the inner body 50. At this time, the amount of heat generated from the billet 85 varies depending on sectional shape and position. Thus, a large amount of cooling water is allowed to flow at a position where the amount of generated heat is great, while a small amount of cooling water is allowed to flow at a position where the amount of generated heat is small, so that the entire billet 85 may be cooled uniformly. If the billet 85 is not cooled uniformly, it is impossible to obtain alloy with uniform tissues, which may cause cracks in a severe case.

The amount of cooling water can be controlled by changing the number or size of the cooling water discharge channels 56, as explained above.

It would be apparent that the scope of the present invention is not limited to the aforementioned embodiment but defined by the appended claims and those skilled in the art can make various modifications and changes thereto within the scope of the invention defined by the claims. 

1. A mold for air-slip type noncircular continuous casting, comprising: a mold body having a noncircular through hole, the noncircular through hole allowing molten metal to move therein; a porous graphite ring provided on an inner circumference of the mold body to supply gas and oil to a surface of the lowering molten metal thereby solidifying the molten metal into a billet; and a conveying plate provided on the inner circumference of the mold body on top of the graphite ring to convey the molten metal downward, wherein a cooling water chamber is formed in the mold body to store cooling water for cooling a surface of the billet, the cooling water chamber being formed in the rear of the graphite ring, and a gas inlet and an oil inlet are connected to an upper end of the graphite ring to respectively supply gas and oil into the graphite ring through the mold is body.
 2. The mold as claimed in claim 1, wherein the cooling water chamber is formed such that an upper end of the graphite ring is higher than a lower end of the cooling water chamber and a lower end of the graphite ring is lower than an upper end of the cooling water chamber.
 3. The mold as claimed in claim 1, wherein the cooling water chamber is formed such that an upper end of the graphite ring is lower than an upper end of the cooling water chamber and a lower end of the graphite ring is higher than a lower end of the cooling water chamber.
 4. The mold as claimed in any one of claims 1 to 3, wherein the mold body includes: an upper body defining an upper portion of the chamber and having a lower surface supporting an upper surface of the graphite ring, the upper body being formed with a gas inlet and an oil inlet for respectively supplying gas and oil to an upper portion of the graphite ring; a lower body defining a lower portion and an outer side portion of the mold body; and an inner body coupled with the upper body and the lower body to define an inner side of the mold body and having a seat portion formed on an inner circumference thereof to allow the graphite ring to be seated thereon.
 5. The mold as claimed in claim 4, wherein the graphite ring has an upper surface supported by the upper body and side and lower surfaces seated on the seat portion of the inner body and fixed to the mold body.
 6. The mold as claimed in claim 5, wherein an asbestos gasket is provided between the graphite ring and the upper body.
 7. The mold as claimed in claim 6, wherein the graphite ring is divided into a plurality of pieces.
 8. The mold as claimed in claim 7, wherein an inner circumference of the graphite ring has a tapered shape whose width is widened as it goes downward to cope with the changed amount of billet that is changed by solidification contraction.
 9. The mold as claimed in claim 8, wherein the lower body has cooling water discharge channels for supplying the cooling water of the cooling water chamber to the billet.
 10. The mold as claimed in claim 9, wherein the cooling water discharge channels are formed to have different diameters depending on the amount of heat generated from the billet.
 11. The mold as claimed in claim 9, wherein the cooling water discharge channels are formed to have different densities at every portion of the inner body depending on the amount of heat generated from the billet.
 12. An air-slip type continuous casting method of aluminum alloy, in which molten metal is solidified while passing through an inner surface of a conveying plate and a graphite ring, thereby producing a billet with a noncircular cross section, the conveying plate and the graphite ring having a tapered shape and being installed on an inner surface of a noncircular through hole of a mold body, the method comprising the steps of: forming a film on a surface of the molten metal being solidified by gas and oil introduced from an upper portion of the graphite ring; cooling the graphite ring by cooling water of a cooling water chamber provided in the rear of the graphite ring; and allowing a borderline of the solidified billet and the molten metal to be in contact with an inner surface of the graphite ring.
 13. The method as claimed in claim 12, wherein the billet is cooled by the cooling water, the cooling water being supplied from the cooling water chamber and ejected through cooling water discharge channels in a lower portion of the graphite ring.
 14. The method as claimed in claim 13, wherein the cooling water is ejected in different amounts depending on the amount of heat generated according to a shape of the billet to be cast.
 15. The method as claimed in claim 14, wherein the amount of the cooling water is determined by the number of the cooling water discharge channels.
 16. The method as claimed in claim 14, wherein the amount of the cooling water is determined by size of the cooling water discharge channels. 